The updated TIA iOS app went live in the App store earlier this week. It has changed names to TIA Learn, but I think it should still just update the existing app on your device through the App store if you already have it. There's a link in my signature, or it will probably be the first hit if you search the App store for the full name "The Infinite Actuary".

Updates to the new Learn app include:

Download unlimited videos to your device for offline viewing

Fully optimized for all iPhone and iPad models

Stream videos over WiFi or cellular data with option to download videos over WiFi only

Track your progress as you watch lesson videos

See all downloaded (offline) videos in one place (like making a “playlist”)